Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Roger L. Stockbauer

Abstract

The oxidation of Mg(0001) was studied using ESDIAD (Electron Stimulated Desorption Ion Angular Distributions), LEED (Low Energy Electron Diffraction) and STM (Scanning Tunneling Microscopy). Disassociated oxygen and two species of oxygen were observed morphologically by STM and were identified as incorporated oxygen (mixed layer) and ionic oxide MgO(111). We observed that the step terraces and the dissociated oxygen are highly mobile and interact easily with the STM tip at room temperature. The true oxide was first observed on a double step pinning site as a protrusion elongated along the step edge. These sites pin the top terrace to the one underneath forming a double step at the pinning site. A form of oxygen (incorporated) characterized by bumps of 1.2 A in height was observed on the plane of terraces. The bumps and protrusions grow in area and height as a function of oxygen exposure. At 12 L oxygen exposure, bumps coalesce to completely cover the surface. By 13 L, LEED show a diffuse 1 x 1 pattern indicating this growth was in registry with the Mg substrate. At larger oxygen exposures, most of the bumps observed are precursors for the formation of protrusions which leads to the thickening of the oxide. ESDIAD indicates that the initial oxygen is subsurface and that the step edges are not involved in the ion desorption. Formation of the oxide surface was complete by 200 L exposure.

Pages

68

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